1. Field of the Invention
The present invention relates to a non-contact ink developing method by which an electrostatic latent image is developed with an ink without contacting it.
2. Discussion of the Related Art
As a method for developing an electrostatic latent image formed on an electrostatic latent image formation member such as an electrostatic recording material or light-sensitive member for electrophotography, the dry developing method using powdered developer and the wet developing method using liquid developer are known.
The wet developing method uses liquid developer consisting of a dispersion medium of high electrical resistivity and toner particles with the opposite charge to the latent image. While bringing the liquid developer in contact with the surface of an electrostatic latent image formation member, the toner particles move by electrophoresis and adhere to the electrostatic latent image to develop it. A fusing process is unnecessary for this method, or even if necessary, a fusing process using a simple fuser is sufficient. Therefore, a compact and inexpensive developing apparatus can be provided compared to an apparatus employing the dry developing method, and moreover, an image of high resolution can be obtained.
However, the wet developing method inevitably uses an organic solvent having flammability and/or volatility as the dispersion medium for the toner particles. Because many organic solvents are toxic to one degree or another, this is undesirable from the viewpoint of safety, and environmental and and health considerations. Furthermore, since the electrostatic latent image formation member is dipped into the liquid developer in the wet developing method, the surface of the electrostatic latent image formation member is gradually contaminated by excess toner particles, which causes attachment of toner to areas other than the electrostatic latent image, and leads to fogging.
To overcome the problems described above, a new developing method has been suggested in which an electrostatic latent image is developed with a liquid ink.
For example, Japanese Patent Application Unexamined Publication No. Sho. 58-215671 (1983) discloses an ink mist developing method which oscillates a liquid ink by an ultrasonic oscillator to generate an ink mist from the surface of the liquid ink and causes the ink mist to agglomerate adjacent to the surface of the electrostatic latent image formation member. In this manner, the ink mist attaches only to the electrostatic latent image by the electrostatic induction force generated by the charge applied to the ink mist from the electrostatic latent image, thus developing the image.
As another developing method using a liquid ink, Japanese Patent Application Unexamined Publication No. Sho. 62-5283 (1987) discloses an ink jet developing method which uses an ink jet developing means having a slit aperture installed close to an electrostatic latent image formation member and equipped with an electrode applying a voltage of an opposite polarity to that of a latent image. A liquid ink is ejected only toward the electrostatic latent image from the slit aperture to develop the latent image. This method makes it possible to record information by a non-contact developing apparatus without using toner or a carrier as the developer.
The conventional ink developing methods described above resolve the problems in the wet developing method, but they have other problems as follows.
In the ink mist developing method, because it is difficult to apply sufficient charge to the ink mist from the electrostatic latent image and agglomerate the ink mist adjacent to the surface of the electrostatic latent image formation member in a stable way, the ink mist cannot attach to the electrostatic latent image selectively and sufficiently. This prevents exact development without fogging, and moreover, it cannot carry out high speed development.
In the ink jet developing method, it is difficult to develop an image with high resolution because of instabilities in the formation of very small ink droplets. Furthermore, the slit aperture must be installed at a narrow spacing, from some tens of micrometers to one hundred micrometers, from the electrostatic latent image formation member, or the slit aperture is apt to become blocked with the passage of time. Accordingly, installation or maintenance of the apparatus is troublesome. In addition, this method has another problem, in that it is unsuitable for performing high speed development.